MAX11646 Datasheet, PDF (18/20 Pages) Maxim Integrated Products – 2.7V to 3.6V and 4.5V to 5.5V, Low-Power, 1-/2-Channel, 2-Wire Serial, 10-Bit ADCs

2.7V to 3.6V and 4.5V to 5.5V, Low-Power,
1-/2-Channel, 2-Wire Serial, 10-Bit ADCs
Transfer Functions
Output data coding for the MAX11646/MAX11647 is
binary in unipolar mode and two’s complement in bipo-
lar mode with 1 LSB = (V_REF/2^N) where N is the number
of bits (10). Code transitions occur halfway between
successive-integer LSB values. Figures 12 and 13
show the input/output (I/O) transfer functions for unipo-
lar and bipolar operations, respectively.
OUTPUT CODE
11 . . . 111
11 . . . 110
11 . . . 101
FULL-SCALE
TRANSITION
MAX11646
MAX11647
00 . . . 011
00 . . . 010
00 . . . 001
00 . . . 000
012 3
INPUT VOLTAGE (LSB)
FS = V_REF
ZS = GND
1 LSB = ^VREF
1024
FS
FS - 3/2 LSB
Figure 12. Unipolar Transfer Function
Layout, Grounding, and Bypassing
Only use PCBs. Wire-wrap configurations are not rec-
ommended since the layout should ensure proper sep-
aration of analog and digital traces. Do not run analog
and digital lines parallel to each other, and do not lay
out digital signal paths underneath the ADC package.
Use separate analog and digital PCB ground sections
with only one star point (Figure 14) connecting the two
ground systems (analog and digital). For lowest noise
operation, ensure the ground return to the star ground’s
power supply is low impedance and as short as possi-
ble. Route digital signals far away from sensitive analog
and reference inputs.
High-frequency noise in the power supply (V_DD) could
influence the proper operation of the ADC’s fast com-
parator. Bypass V_DD to the star ground with a network of
two parallel capacitors, 0.1µF and 4.7µF, located as
close as possible to the MAX11646/MAX11647 power-
supply pin. Minimize capacitor lead length for best sup-
ply noise rejection, and add an attenuation resistor (5Ω)
in series with the power supply if it is extremely noisy.
Definitions
Integral Nonlinearity
Integral nonlinearity (INL) is the deviation of the values on
an actual transfer function from a straight line. This straight
line can be either a best straight-line fit or a line drawn
between the end points of the transfer function, once offset
and gain errors have been nullified. The MAX11646/
MAX11647’s INL is measured using the endpoint.
OUTPUT CODE
011 . . . 111
011 . . . 110
000 . . . 010
000 . . . 001
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
FS = ^VREF
2
ZS = 0
-FS = ^-VREF
2
1 LSB = ^VREF
1024
MAX11646
MAX11647
100 . . . 001
100 . . . 000
- FS
0
INPUT VOLTAGE (LSB)
*V_COM ≥ V_REF/2 *V_IN = (AIN+) - (AIN-)
Figure 13. Bipolar Transfer Function
+FS - 1 LSB
3V OR 5V
SUPPLIES
V_LOGIC = 3V/5V GND
R* = 5Ω
4.7μF
0.1μF
V_DD
GND
3V/5V DGND
MAX11646
MAX11647
DIGITAL
CIRCUITRY
*OPTIONAL
Figure 14. Power-Supply Grounding Connection
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